The present invention relates to a low drop-out regulator, and more particularly to a circuit for speeding up the activation time of a low drop-out regulator.
Low Drop-out Regulator (LDO) is a well-known DC-to-DC voltage regulator. When a circuit system is power on, the LDO should be controlled to enter a soft-start state before entering the normal state, otherwise an inrush current may be induced. The inrush current may decrease a voltage level of a power supply, which supplies power to the LDO, as the power supply may not be able to generate the large inrush current in such a short time. Then, the decreased voltage level may affect the operation of other circuits connected to the power supply. Therefore, conventionally, when the LDO is power up, the LDO is controlled to enter the soft-start state for reducing or eliminating the inrush current. By doing this, however, the activation time of the LDO is longer. More specifically, if the soft-start operation of the LDO is controlled by a soft-start circuit, then the soft-start circuit may limit the supply current of the LDO to limit the inrush current during the soft-start state. If the soft-start circuit decreases the supply current of the LDO during the soft-start state to reduce the inrush current, the activation time of the LDO becomes longer. As the quiescent current of the conventional LDO may decide the activating current of the conventional LDO during the start up period, improving the activation time of the LDO may worsen the power consumption of the LDO by using the conventional ways. Therefore, there is a need to solve the above-mentioned problem by providing a fast activated and low power consumed LDO.